With feature sizes in semiconductor technologies getting increasingly smaller, the wavelength of light has become a limiting factor in optical processes used in semiconductor processes, including lithography and wafer and mask inspection and metrology. Advanced optical technologies use EUV light (for example, wavelengths in the range of 11 nm to 15 nm and more specifically wavelengths of 13.5 nm) to address issues resulting from increasingly smaller features sizes, and a bright EUV light source free of debris is invaluable in the pursuit of next generation semiconductor processes. One challenging aspect of developing a bright EUV light source is to mitigate debris from the plasma generation process while minimizing the loss of EUV light produced by the plasma.
The generation of EUV radiation useful for these semiconductor processes involves the production of high-temperature plasma, such as laser-produced plasma (LPP), discharge-produced plasma (DPP), and laser-discharge produced plasma (LDP or laser-initiated DPP), which can emit light having the desired wavelengths for advanced optical processes. In LPP, a high energy laser is focused at a source material to ionize the source material, thereby generating high temperature plasma that emits EUV radiation. In DPP, source gas is flown through a system and high powered Z-pinch pulse compression is applied to ionize the source gas and produce high temperature plasma that emits EUV radiation. In LDP, a laser is used to initiate the conditions necessary to perform DPP generation by first vaporizing a source material. Producing plasma using the aforementioned techniques to create a useful EUV light source presents a challenge because the plasma generation process produces debris in the optical path of the EUV light, which causes damage to the EUV optics and diminishes their useful lifetime.
One way to mitigate debris is by means of pressurized gas, other than source type gas used to fuel the discharge, which is injected across the path of EUV light. For example, mitigation has been done by stationary plasma. However, gas alone is not effective on a majority of the debris emitted (ions, particles). Another method to mitigate debris is to apply a DC voltage, magnetic fields and plasma. However, steady state DC and plasma can further energize ions created in the production of EUV light. Their energies can be increased and the damage can be enhanced.
Some methods have been used to mitigate debris from EUV light sources while also providing the gas fuel to the discharge. For example, pressurized gas can be combined with quiescent feed or feed from behind the light source to fuel the plasma. Fuel gas and mitigation gas are separate. A jet is not used for fill but instead background fill that is lightly pumped is used for this purpose. However, to do this extra gas is required in the system. The extra gas reduces the EUV energy along the optical path. Furthermore gases other than the desired source gas in the source gas also degrade the emission.
For the methods discussed above, ions and particles emitted from the generated plasma have to be removed from the path by additional engineering measures that decrease the EUV light transmission. Accordingly, it would be advantageous to develop effective methods and system to achieve debris mitigation and source fueling for EUV light sources that overcome these disadvantages.
It is within this context that aspects of the present disclosure arise.